1. Field of the Invention
The present invention relates to using spectroscopic methods in medical diagnostics to analyze and diagnose specific bacteria in a biologic sample. Using this diagnostic technique, specific bacteria can be identified sooner and without culturing, and bacteria-specific antibiotics can be prescribed sooner, resulting in an earlier, more accurate diagnosis of infection and corresponding antibiotic prescription, decreased likelihood of antibiotic resistance and an overall reduction of medical costs.
Middle ear infection, or otitis media (OM), is the most frequent diagnosis in children. Seventy-five percent of children under age three experience at least one episode of otitis media, while almost half of those children will have three or more infections.
OM accounts for almost 46% of the more than 48 million annual prescriptions in the United States. The estimated cost of treating OM is about $5 billion annually.
OM is a bacterial infection that results in inflammation of the inner ear and an accumulation of fluid behind the eardrum. Usually resulting from a bacterial or viral infection secondary to a cold, sore throat, or other respiratory infection, OM is usually treated with antibiotics. A diagnosis of the specific bacteria results in targeted treatment by helping physicians prescribe an antibiotic effective for the particular bacteria.
Current medical methods used to diagnose bacterial organisms normally require at least one day. In addition, physicians often need to determine bacteria resistance to antibiotics, and this determination routinely takes another day. Gram staining, analyzing organisms from a sample visually with a microscope, may provide a rough estimate of the most likely organism, but this process can be inaccurate. This is especially so for one of the bacteria common to OM, Haemophillus influenzae. Thus, after a presumptive diagnosis from gram staining, the bacteria are cultured for at least a day and identified. This time-intensive process follows the difficulty of acquiring the sample from the patient. The methods of collection depend on the site of infection. Some are readily accessible, such as urine, however some samples require invasive procedures which can be quite painful, including, in the case of OM, piercing the eardrum to withdraw infected fluid. Additionally and unavoidably, some samples are collected after the patient has begun antibiotic treatment, making diagnosis of the bacteria organism difficult or impossible.
Because of the delay in specific bacterial diagnosis and the pain suffered by the patient, physicians usually prescribe broad spectrum antibiotics that can cover a wide variety of bacteria until the specific strain of bacteria is identified. After identification, the antibiotics are usually changed to those necessary to treat the infection. In the case of OM, the physician will treat with antibiotics to cover the most likely organisms, and if the organism is resistant to the antibiotic, the physician will change the antibiotic after the patient fails to improve over a few days. In cases where a specific bacterial diagnosis is impossible, treatment with broad spectrum antibiotics is continued.
There is a growing concern in the medical field over developing antibiotic resistance. Bacteria can develop resistance to antibiotics when they are exposed to them through several mechanisms. They also have the ability to pass this resistance on to other bacteria that have not been exposed to the antibiotic. As a result, physicians prefer to use the simplest antibiotic necessary to treat an infection, thus reducing the exposure of bacteria to stronger antibiotics and theoretically reducing the rate of resistance.
Therefore, there exists a need in the art for methods for rapidly diagnosing bacteria, thus improving patient care by providing targeted antibiotic therapy earlier. Rapid diagnostic tests can decrease antibiotic resistance by decreasing the use of broad spectrum and ineffective antibiotics. Medical costs may also be lowered since fewer prescriptions would be changed during treatment.
2. Prior Art
Some spectroscopic techniques already known in the art have been adapted for use in medical diagnostics, none of which provides the advantages of the present invention. For example, WO 97/48329 discloses a method for diagnosing cervical precancer using near infrared Raman spectroscopy. Additionally, several spectroscopic techniques are already used to detect bacteria in isolated samples.
Goodacre et al. disclose the use of pyrolysis mass spectrometry (PyMS), Fourier transform infrared spectroscopy (FTIR) and dispersive Raman microscopy to analyze a group of bacterial isolates associated with urinary tract infections. (Microbiology May 1998, 144 (Pt.5): 1157-70).
WO 98/41842 discloses a system for the detection of bacteria antibody complexes using UV resonance Raman spectroscopy. The system uses Raman spectroscopy to create a characteristic spectral peak of a microorganism analyzed from an antibody complex.
Werkhaven et al. disclose that an optical window that will transmit sufficient light for in vivo measurement of fluorescence profiles has been found in the chinchilla tympanic membrane. (Laryngoscope March 1994; 104(3 pt. 1): 264-8).
Sorrell et al. disclose that fluorescence profiles of four common pathogens have been determined and are reproducible. (Lasers Surg Med 1994; 14(2): 155-63.
Timmins et al. disclose that distinct fingerprints for three Candida species are consistent with reference isolates. (J. Clin. Microbiol. February 1998, 36(2): 367-74).
In the above studies, the identification of bacteria using Fourier-transfer infrared spectroscopy (FTIR) has only been demonstrated for isolated bacteria after they have been cultured and purified. The ability of FTIR spectroscopy to detect bacteria in biologic fluid has not, heretofore, been investigated.
Biologic fluid has absorption bands that greatly overlap the regions useful in differentiating the differences in bacteria. Such overlap would greatly change the previous general analysis and conclusions of the spectroscopic techniques. Furthermore, the biologic fluid might interact chemically with the chemicals in the bacteria or alter the local environment of the bacteria (i.e., by changing the pH) sufficiently to alter the spectra of the bacteria and make them unrecognizable when compared to their pure spectra. Therefore, it is necessary to be able to study the spectra of the bacteria in the biologic fluid, that is, in samples taken directly from the patient. In addition, it becomes more practical to analyze the spectra of bacteria within the context of one disease entity at a time. This specifies the nature of the medium and simplifies data interpretation by limiting the number of possible pathogens. None of the above-described techniques address these considerations.
The present invention, on the other hand, is directed to a method for using spectroscopy in the identification of specific bacteria in a biologic sample. Preferably, FTIR is used to detect the three most common bacteria in otitis media (OM), Streptococcus pneumoniae (SP), Haemophilus influenzae (HI) and Morazella catarrhalis (MC).
Briefly described, in a preferred form, the object of the present invention is to provide a method for the diagnosis of a bacterial organism in a biologic fluid using spectroscopic techniques. Preferably, FTIR, fluorescence and Raman spectroscopy are used as medical diagnostics to detect the three most common bacteria in otitis media (OM), Streptococcus pneumoniae (SP), Haemophilus influenzae (HI) and Morazella catarrhalis (MC).
It is a further object of this invention to provide a diagnostic method for detecting specific strains of bacteria in a biologic sample without subjecting the sample to culturing. Preferably, FTIR, fluorescence and Raman spectroscopy are used to detect bacteria. More preferably, FTIR is used to diagnose the bacteria.
It is another object of the present invention to improve the treatment of infectious diseases by providing a rapid strain-specific bacterial diagnosis. By increasing the speed of diagnosis of the specific strain, a doctor may immediately begin targeted treatment of the infection with an antibiotic specific to that strain.
These objects have been achieved by using spectroscopic techniques such as FTIR, fluorescence and Raman spectroscopy to compare the known spectra of particular bacteria strains with the spectrum determined from a biologic sample and subtracting the spectrum of pure serum.
More particularly, the present invention is directed to a method for diagnosing bacteria in a biologic sample comprising analyzing a sample of infected serum with a spectrometer, subtracting the spectrum of a previously-obtained reference serum from the spectra of the infected serum, and comparing the resulting differential spectra with reference spectra of bacteria in saline to determine the specific bacteria present in the sample.
It has been found that using our spectroscopic techniques, a rapid determination of the specific bacterial strains can be made, thus allowing for targeted treatment and avoiding the use of broad spectrum antibiotics. Such targeted treatment eliminates the medical costs associated with prescribing broad spectrum antibiotics and then represcribing antibiotics specific to the infection. Additionally, targeted treatment reduces the likelihood of the patient developing antibiotic resistance.